Mineral. Deposita (Berl.) 4, 260--274 (1969)

Barite Deposits of the "Montagne Noire", Southern France

THOMAS HOFFMANN

Labora to r ium fiir Sedimentforschung, Mineralogisch-Petrographisches Inst i tut der Universit/ i t Heidelberg, West -Deutschland

, , . . . es ist zwar nicht sinnlos, aber doch etwas unlogisch, wenn man yon vornherein nicht ver- sucht, eine Lagerst~tte in ihre Umgebung auf die wahrscheinlichste Art einzugliedern, sondern sie unbedingt einem ganz fremden, zun~chst nicht von selbst verst~ndlichen Bildungsvorgang zuordnen will." H. SCHNEIDERHOHN (1954)

Several small barite deposits of Devonian age are known in the Monts de Cabri4res region, Montagne Noire (southern France). A field and laboratory investigation of these stratabound deposits showed their possible diagenetic origin and a limited economic value.

De petits gisements de barytine du D4vonien dans les Monts de Cabri4res (Montagne Noire, France) out 6t6 &udi6 en d&ail sur le terrain et au laboratoire. Les observations out apport6 des crit~res pour une explication g4n&ique de ces gisements <(stratiformes>>. Ils indiquent que les concentrations min~rales se sont effectu4es par un processus de s&r&ion au cours de la diagen&e. L'im- portance &onomique de ces gisements est limit6e.

I. I n t r o d u c t i o n

The barite deposits described in this paper are located in the Monts de Cabrihres, a part of the Montagne Noire in Southern France. In this area the strat igraphic column extends f rom the Lower Ordovic ian to the Lower Triassic. But in general the barite deposits are confined to the Lower /Midd le Devonian only (Figs. 1 and 2). The structure consists of an intensively imbricated sequence of small nappes, largely due to a variable response to tectonic stress of rock units wi th different l i thological nature. This is what GALLWITZ (1956) called tectonic selection. Details on the regional and local geology are found in GEZE (1949), MAUREL (1965), HOFF- MANN et PUSCHMANN (1967), BOYeR et al. (1968), and HOFFMANN (1969). The Informa- t ion given in this paper is l imited to details per t inent to the barite deposits.

These deposits have been given little at tention in the past. RAGUIN (1949, p. 317) briefly ment ioned barite occurrences in this area and assigned a hydrothermal formation. OVTP, ACHT (1959) studied similar barite deposits in Lower Devonian strata in the Massif de Mouthoumet (southern France) which are equivalent to the present formations and postulated also a hydro- thermal origin. CHERMETTE (1962), dealing with the Mts. de Cabri~res deposits interpreted them as being a result of hydrothermal solutions precipi tat ing in an already existing karst region. I t should be ment ioned that Devonian strata in southern France (Montagne Noire, Massif de Mouthoumet , Pyren&s) are generally miner- alized, often in barite. A search of the l i terature for reports of similar deposits in the wor ld indicated that such deposits are common hut had not been de- scribed in detail. These kinds of deposits have been considered, until recently, to be of

TH. HOFFMANN, Barite Deposits of the "Montagne Noire", Southern France 261

VILLENEUVETTE []

( Studied area \

"L,

/

[ ~ UNDIFFERENTIATE~

TRIASSIC

17L =] UPPER PERMIAN

[77."7]. LOWER PERMIAN

UPt? C,4RBONIFERO

LOWCARBONIFER. & LIMEST,-LENSES

UPRDEVONIAN

MIDDLE DEVONIAN

LO W DEVONIA N ORDOVICIAN

BASAL TES ( TERTIAf

DOLERITE DYKE

PORPNYR.ANDESITt

[] Eg~]

E 3 E23

r ~ l

r-dn

F ~ r~q

r - ~

Feq

SILURfAN SCt~ISTS

BARITE EXPLOITAT,

BARITE OCCURREN

aUARrZ-veto : : : :. :-7,4}i:" MAJOR ACCIDENT

N EFFI E S . ' , '

b 1: la Rouquet te

½km 2: [a Rossignole 3 : [a Boissi~re 4 = Font d'Arques

Fig. 1. Geological map of the MTS. de Cabri&res area preliminary results

hypogene metasomatic origin. A study of the unpublished data of LmasAcc~i (1959) on the Potosi Missouri deposits (material available in the collection of G. C. AMSTUTZ) shows these deposits to be similar and in many respects identical with regard to composition, para- genesis and fabric.

II. Out l ine of Barite Occurrences (Observat ions)

Barite deposits are encountered in several tectonically detached units of the Mts. de CabriEres, generally in the upper part of Lower Devonian dolomites, for instance, at "la Rouquette", "Font d'Arques" and "la Ros- signole" in the vicinity of Cabrihres, and at

"la Boissi~re" near Peret. Barite-bearing strata generally strike E - W and dip southward. In one place only, on the southern slope o£ the hills of "les Serres" (W route D 124, N FontEs), barite occurs in a conglomerate containing chert pebbles which indicate a post-Visden age (Lower Carboniferous) of this conglomerate. Near a pit of "Font d'Arques" (Villeneuvette Sud), Devonian dolomites are covered by red argilaceous, unconsolidated sediments of re- stricted extent, presumably of Tertiary age. At one time barite was mined from these sediments. The country rock containing the barite consists mostly of dolomites of Lower Devonian age. In some places dolomitic strata of Middle and even Upper Devonian age may show poor barite occurrences. Only once, as mentioned

262 TH. HOFFMANN

~q

F~3 F~q

F~

Oenere l i zed Co lumnor Sect-ion Mrs. de Cobr i~res-region

TRIASSIC

PERMIAN

UPPER CARBONI =

FEROUS

West East" r

LOWER CARBONIFER. ~ ~ 4--~.~.~-- ev : .~-.~ UPRDEVONIAN ~ . .@~. -~ - .~ -~ .~ . .

MID.DEVONIAN ~ ~ ~ _ _ , ~ _

mW.DEVON~AN --~T~-~-~-~--~

2" ASHBILL ,,~ CARADOC ,~ LLANDEILO ~ L ~ O ARENIG g TREMADOC O

GRAPTOLITIC SHALES ~ PORPHYRITIC ANDESITE

INTERLAYERED CLAYST. CALCAREOUS SILTSTONE - SANDSTONE SANDSTONE

GRAYWACKE, 1 ~ LIMESTONE LENSES SANDSTONE

SANDSTONE MASSIVE BEDDED CONGLOMERATE DOLOMITE CONGLOMERATE OF MEDIUM TO THICK

1"~'31 BEDDED LIMEST. Q - PEBBLES CONGLOMERATE OF LIMESTONE - MARL LIMEST.-PEBBLES FLAGGY BEDDED CWERTS V ~ LIMESTONE COAL F ~ MASSIVE LIMESTONE

BARITE BODIES

Fig. 2. Generalized columnar section MTS. de Cabrieres-region

STRATIGRAPHICAL BREAK

p ~ VARISCIAN OROGENY GERMANOTYPE

OROGENY

above, was barite found in a younger forma- tion. HOFFMANN et PUSCH~ANN (1967) described the lowest part of the Lower Devonian sequence in detail. I t starts with sandstones and quartzites, partly altered by silicification, or with sandstones with a dolomitic cement (dated paleontologically as Lower Devonian), or, in some places, with brecciated and silicified dolomites. These three facies grade laterally into one another, ranging in thickness f rom approximately 2 m to about 25 m. They are overlain by massive dolomites of roughly 100 m thickness. In some places, white quartzite

pebbles have been observed in the lowest portions of the dolomites. In the upper portions thin intercalations of argillaceous limestones are common and mark the boundary between Lower and Middle Devonian. Concentrations of barite are most commonly found near and above this transition zone. Sedimentation appears to have taken place in a relatively shallow part of the ocean, perhaps in an area with lagoons, because rapid facies changes in time and space are observed. Brachiopods and Crinoids reveal moreover that the environment was without doubt marine. A reconstruction of the paleogeography would be

Barite Deposits of the "Montagne Noire", Southern France 263

difficult on account of the complicated tectonic imbrication. Volcanic activity is known from Ordovician, Permian and Tertiary time. The Devonian beds are devoid of any trace of volcanism. In summary, silica rich horizons of limited vertical thickness are found at the bottom, followed by a transitionary zone and massive dolomites above. In lateral extension, dolomiti- zation continues but with variable intensity.

The upper limit shows irregular fronts of dolomitization. In some places not only the Lower Devonian and parts of the Middle Devonian, but also the Upper Devonian strata have been dolomitized.

Tectonically, the area is intensively faulted and overthrust as stated in the introduction. None of these thrust planes, fractures and faults shows, however, any sign of mineralization.

N $ 0 50 cm

Fig. 3. Villeneuvette Sud, irregularly shaped barite masses in dolomite

264 TI~. HOFFMANN

/ / ~ ~ ( - , ~ ~ - i.. __~...r

1 :

Sw RE 0 ¢a_1 m 100

Fig. 4. Open pit west of Villeneuvette Sud exploitation, elongated barite masses, subparallel to dolomite strata

Barite occurs as nests, pockets , chain-like l inked, smaller or larger coherent masses. The shape and the dimensions of these barite con- centrations are thus very irregular. Their sizes range f rom millimeters to centimeters or to several or even tens of meters in diameter. Commonly, lenticular masses are g rouped together (Fig. 3). Strictly isolated occurrences are less common. When bedding can be dist inguished in the generally massive dolo- mites, bari te occurs statistically parallel to it.

The dimensions of the irregularly shaped barite masses measured parallel to the layering are often two or three times as great as that measured vertically (Fig. 4). In the case of thicker masses of bedded bari te or of lenticular masses of very elongated shape, they very often fol low deformations of the dolomit ic country rock. Larger barite masses commonly show breccia-like structures with angular to sub- rounded dolomite elements irregularly dis- t r ibuted in a bari te matrix (Fig. 5). In detail,

Barite Deposits of the "Montagne Noire", Southern France 265

W , ~ E

0 30cm

Fig. 5. Villeneuvette Sud exploitation, dolomite elements of angular to subrounded shape are irregularly distributed in barite matrix

a relay-like contact between different dolomite constituents is seen and we define this structure as a relay-like brecciated structure. By this we mean that large isolated barite bodies are linked together by long thin stringers (Fig. 6). In addition barite was found with argil- laceous interstratifications of the essentially dolomitic sequence. I t is mostly of nodular shape and is associated with fluorite (Fig. 7). On a local scale, veins or veinlets connect barite pockets and dolomites (Fig. 3). As mentioned above, barite occurs in a Triassic basic conglomerate, where barite forms en- velopes around dolomitic and quartzitic pebbles or is included in some pebbles or forms string- ers in the matrix of the conglomerate (Fig. 8). In summary we have:

a) Irregularly shaped barite masses in a dolo- mitic country rock, or, on the contrary, nests of dolomite in barite masses (Figs. 3, 4, 5, 6) or barite together with fluorite in argillaceous interstratifications (Fig. 7).

b) barite filling fissures (Fig. 9);

c) barite in a Triassic conglomerate (Fig. 8).

Generally, the barite is of high purity, white and well crystallized. The crystals are largely developed in tabular form and rosettes follow- ing (001). Aggregates with crystals longer than 20 cm are common. Elongated, pris- matic, yellow crystals occur in geodes of dolomite.

266 TH. HOFFMAN>:

s 6

Fig. 6. Villeneuvette Sud exploitation, "relay - - l i k e brecciated structure"

N 16o¢r.

Fig. 7. Villeneuvette Sud, barite and fluorite in argillaceous interstratifications

Barite Deposits of the "Montagne Noire", Southern France 267

/

q ~ q

Fig. 8. Southern slope of 'les Serres' hills, barite as an element in Triassic conglomerate

Fig. 9. Open pit west of Villeneuvette Sud exploitation, barite vein; hammer indicating strike and dip of bedding plane

268 TH. HOFFMANN

The mineral assemblage is quite simple since barite and dolomite are almost always the only minerals observed. The contacts between these two minerals are generally sharp although they may be highly irregular and barite normally grows in the country rock dolomite. Some- times fluorite is found together with barite, for instance in the quarry of "Font d 'Arques" (Fig. 10). This quarry is of particular interest because of the occurrence of small crystals of chalcopyrite in larger aggregates of barite (Fig. 11). Barite assemblages are found here which show a color zoning in different shades of greenish-blue, due to the alteration of copper minerals to secondary malachite. An association of barite with sphalerite was observed only once in the abandoned pit of "la Rouquette". Several specimens showed stylolite-like contacts between honey-colored sphalerite crystals and barite, suggesting perhaps a similar paragenetic age for these two minerals. In former times, copper was extracted from an occurrence near the present barite deposit of "la Rossignole".

Sample Locality 3a4S -- Value in °/o 0 No.

ROU La Rouquette 15.9 P N of Neffi~s 16.9 PER Peret 18.0 ROS 1 La Rossignole 18.2 ROS 2 La Rossignole 20.4 VI Villeneuvette 19.2 BRO Vallfie du Bronc 20.4

The total error is estimated to be about 0.2°/00. These data will be discussed later.

For reasons shown by PUCHELT (1960), the Sr-concentration in barite samples f rom distinct localities in the Mts. de Cabrihres region has been determined by Dr. H. PUCHeLT (Tiibin- gen). It was measured directly together with the total amount of Ba- and Sr-sulfates. From these values the Ba-content and the Ba/Sr ratio were calculated. The results are as follows :

Sample Locality Remark Ba % Sr % BaSO 4 + SrSO~ Ba/Sr computed measured measured computed

ROU la Rouquette Vi Villeneuvette SE b 1 ~ La Serre, envelope of pebble SE c J triassic conglomerate veinlet

56.24 ;~ 0.89 97.45 63 54.77 z 1.13 95.45 49 47.65 ;~ 0.77 82.6 62 50.13 ~ 5.50 96.72 9

Today, the original copper occurrences are not accessible. Only a few small and weathered ore specimens were found on ancient dumps con- taining malachite and azurite in small fissures. F rom the small amount of material available, it has not been possible to consider any genetic relationship between these copper minerals and the nearby barite. Distinctive aa4S-values have been reported for sulfides and sulfates of different age and different origin (hydrothermal or sedimentary) as well. (See for instance NIELSEN 1965, 1968). There- fore, the 8a4S accumulation in barite samples f rom different localities in the Mts. de Cabri&res region has been measured by Dr. H. NIELSEN (G6ttingen). The results are as follows:

I lL Genetic Considerations

Proceeding from large to small scale, the fol- lowing observations may be used to interpret the mode of occurrence of the barite deposits in the Mts. de Cabrihres region (see Fig. 12)!;

1. On a regional scale (100 to 1,000 m), the barite occurs within definite stratigraphic horizons, which represent certain facies in the sedimentary sequence. The term stratabound or even stratiform ore deposit can therefore be applied (compare for example NICOLINI 1965) and on this scale the occurrence of the barite is congruent in the sense of AMSTUTZ (1959, p. 102). The deposition of the barite must be pretectonic since its dis-

Barite Deposits of the "Montagne Noire", Southern France 269

Fig. 10. Villeneuvette Sud, intergrowth of fluorite and barite, dolomite countryrock; fluorite punc- tuated, dolomite in black

Fig. 11. Villeneuvette Sud, small crystals of chalcopyrite together with fluorite and barite; dolo- mite countryrock

270 TH. HOFFMANN

geological map

for symbols see fig.1

0

J Font d'Arques

lO00m

schematic cross-section

Font d'Awues

200m 100 0 Regional scale 10RDOVICIAN 3 MIDDLE DEVONIAN

2 LOWDEVON 4 CARBONIFEROUS BARITE CONCENTRATIONS IN BLACK

I t ~ Dolomite country rock Meter scale (outcrop-scale)

0 lOm

~ l ~ l l l l ~ l l l i t ~ l ~ . ° ~--¢-~ - - Bari'e

~ ~ Dolomite country rock

Centimeter scale o lb cm

Fig. 12. Font d'argues barite deposit large to small observation levels schematically

t r ibut ion is s t ra tabound and not " faul t -bound" . To invoke a mimetic replacement would be against scientific logic (compare AMSTUTZ 1968), since epigenetic diffusions are nowhere known to form congruent patterns. Even if this were not the case, there are, in detail, no single rock types or patches of a nar row composi t ional range known to serve as discrete hosts of the barite. This leads us to the next scale, that of the outcrop.

2. The strat i form character of the bari te distri- but ion becomes less p ronounced on the outcrop scale (meter to decameter scale). The same is true of the bedd ing features as a whole. This means that large masses of rock lack recogniz- able bedding features. Accordingly , the shapes of the barite bodies, globules or lenses - - usually of quite i rregular shape - - also often depart f rom strict "congruency" to that known on a larger scale as bedding. However , in the field it

Barite Deposits of the "Montagne Noire", Southern France 271

is easy to observe that the longer axes of these barite bodies generally are parallel or subparallel to the bedding. Since the dolomite country rock itself is often massive, i.e. without bed- ding, any other rock element forming within this physically homogeneous space would be expected also to show a distribution corre- sponding to the advanced isotropy of this space. One would expect, therefore, a certain irregularity of the barite pockets and stringers. This possibility becomes a certainty if we con- sider the next smaller scale.

3. On this scale (centimeter to meter), the congruence with the bedding is generally lost completely. As new geometric features, occa- sional brecciation, vug-formation or other small-scale diagenetic disintegration features in the massive dolomites are found. Here the barite assumes again a certain congruence, which this time is distinctly different from the large-scale regional congruence. Barite patches of this small size are clustered in elongate patterns or form occasional stringers which look like short, restricted veinlets whenever they extend in a vertical direction, or as thin beds when horizontal. This is the typical geometry of late diagenetic phases and it corresponds to the geometric patterns observed by AMSTUTZ (1964) for late diagenetic pyrite in similar dolomites. Moreover, if barite is late diagenetic, as presumed in this paper, it can migrate in almost any direction provided for a late fluid phase of the diagenetic crystallization system.

In addition, on this scale, the late diagenetic age is evident from the crystallization sequence which indicates barite formation later than dolomitization. The late diagenetic barite formation is also indicated by the orientation of the barite crystals or clusters and aggregates. They grow on the broken and/or once open surfaces of the dolomite breccias and rugs, and the growth orientation is away from these sur- faces, normally concentric into the centers of the breccia or the vugs. Replacement is not likely since the pieces of breccia are sharp and the rugs isolated, i.e. often without connecting channels between them. We reported 8a4S-values of the Mts. de Cabrih- res barites from distinct locations in the range + 1 6 to +21 (average 18.5). The data are in

accordance with those reported for Devonian evaporites in general (compare NIELSEN 1965, p. 167). If the barites were of hydrothermal origin, the values should be considerably lower. NmLSEN (1968) reported for hydro- thermal barites of the Harz region (Germany) values from 0 to + 10. The data on the Ba and Sr concentrations reveal that the first three samples have rather similar concentrations. The Ba/Sr ratio is roughly 50. In spite of the fact that these samples come from distinct places in different tectonic units, the data suggest that the composition of the ore- forming fluids and conditions of localization and deposition have been homogeneous. The relatively high Sr content in a veinlet of a Triassic conglomerate and, consequently, a rather low Ba/Sr ratio is explained by rework- ing processes during formation of this conglom- erate favorizing a Sr concentration with respect to Ba. In the next chapter a theoretical possibility of formation, leading to the high concentration in Ba and Sr, will be discussed.

IV. Discuss ion of Secondary Silicification and Dolomit izat ion in Relation to Barite Concentration

In addition to the genetic considerations, we should mention dolomitization and silici- fication which are observed in these rocks. It would appear that these are linked processes, as the silica-rich rocks always occur below dolomites in the stratigraphic sequence. This spatial differentiation may reflect separa- tion processes involving silica and carbonate in sediments undergoing lithification. The con- stant waterflow during compaction in an up- ward direction is considered as the vehicle of this differentiation process. It has been commonly observed that replace- ment of carbonates by silica has taken place in buried sediments. LOVERING (1962) and StayER (1962) in particular, discussed this phenomenon in more detail. Obviously, dissolution of car- bonates and precipitation of silica are control- led largely by chemical conditions and primarily through variations of concentration and com- position of connate waters and the interaction of buried organic material, as well as bacterial activity. The high concentrations needed for

272 TI~. HOFFMANN

8

o~ ~ 'a .- o, = - , ° ~ - ~ 8

.1210 • ~: ~ ~ o 2 ~ ~m

9 0 o o < ' T - bOq) t/)¢O men , [[~ Y l , v l l / I [1

iiiirlii

.o

o Z

-5o~ ~IVNIII

~ e a m m l

7 o

"6

0

Changes in composition of pore waters as a resu[t of wdter of compaction passing through semiperrneab[e membranes (rnod[f[edofter SIEVER, 1962)

Fig. 13. Changes in composition of pore waters as a result of water of compaction passing through semipermeable membranes (modified after SleVER •962)

the replacement mechanism can be achieved in the buried sediments by the effect of clay- membrane filtering together with the water- flow of compaction (DE SITTER 1947; VON ENGELHARDT 1961; SreVER 1962; PUCHELT 1964, 1968), as explained in Fig. 13. Spatial separation can be explained by the fractional dissolution and precipitation capabilities of carbonates and silica. Following PUCHELT (1968) and USDOWSKI (1967), normal seawater, as trapped in marine sediments, can be considered as the mzin ma- gnesium source for diagenetic dolomitization. Sufficiently high concentrations in the brines, necessary for the formation of interstitial dolomite, are easily achieved by argillaceous interlayers acting as clay membrane filters. GEZE (1949b) studied dolomitization in the Montagne Noire region. On the origin of the Lower Devonian dolomites he concluded (p. 115) that they should be considered as epi- genetic, though dolomitization occurred shortly after the calcareous sedimentation. JavoY et FAYARD (1966) studied fronts of dolomitization in the Devonian of the Mon- tagne Noire and they concluded that dolo- mitization through an input of magnesium derived from trapped normal seawater was

impossible. They also excluded the possibility of dolomite formation by separating mag- nesium-rich carbonates and finally suggested (p. 85) "le caract~re brutal de la s4paration calcaire - - dolomie sugghre plut6t une circu- lation d'eau ~t travers le s6diment (ou la roche), avec intervention d'une concentration limite au dessous de laquelle la transformation ne pouvait plus se produire". This dolomite formation can now be better understood by introducing the combined concepts of mem- brane filters and waterflow of compaction. The general absence (with few exceptions) of dolomitization in the marls and marly lime- stones of the overlying Middle and Upper Devonian is compatible with this theory. Consequently, secondary silification (explained as replacement of carbonates by silica) and dolomitization can be considered as diagenetic processes. It is felt that barium (and strontium) concen- tration and precipitation can also be explained as diagnetic processes. According to PUCHELT (1963, 1968), dissolved BaSO 4 of continental origin may precipitate at the entry of the sea, as in a marine environment the solubility of tdaSO 4 is very low. As a result of brine for- marion (following Fig. 13), finely disseminated

Barite Deposits of the "Montagne Noire", Southern France 273

barite undergoes redissolution and sulfates disappear simultaneously, due to reduction of sulfates by bacterial attack. This is what Pu- CrlELT (1964) calls "bakteriell bewirkte Lateral- sekretion" (bacterially induced lateral secre- tion). For example, a very high content of dissolved barium and no sulfates in connate waters has been reported by PUCHELT (1964) for the brines of the Ruhr coal-mining district, where no hydrothermal influence exists. Final sulfate precipitation is possible when such up- flowing brines encounter sulfate-rich waters, e.g. normal sea water. Due to the relatively late redissolution of barite, precipitation can occur also in small faults and fissures already developed in the sediments reaching final lithification, as mentioned before. These faults on the other hand may act as channel-ways for solutions rich in barium, explaining crosscut- ting features in barite deposits.

VI. Conclusions

From observations in the field it was concluded that the Mts. de Cabribres barite deposits should be described as strata - - or facies - - bound. To draw conclusions on their origin, observations made from large to very small scale were dis- cussed from genetic points of view. Finally, the theoretically inferred diagenetic processes of secondary silification, dolomitization and barite concentration have been briefly reviewed. In summary it is concluded that

a) geometric parameters are largely congruent and suggest a sedimentary origin,

b) throughout diagenesis localization of silica, dolomite and barite with or without fluorite took place in this order,

c) diagenetic crystallization and/or recrystalli- zation took place subsequently, leading to the present grain sizes,

d) there is no tectonic control of mineralization,

e) the barite bearing dolomites originated in a marine lagoon environment.

The late diagenetic age of barite causes a large variation of depositional textures including crosscutting features. This may create the impression that the barite bodies have been localized during different stages. This latter possibility should not be excluded. However,

to date, no definite indications hay%been ob- served, except as described. The fact, that neither small nor large tectonic planes contain barite suggests that the larger tectonic events were not contemporaneous with, or a cause of barite remobilization or localization. Barite concentrations appear to be somewhat facies-bound and of limited extent; but the facies-factor cannot he defined accurately as yet. Consequently, a more specific metallotect in the sense of ROOTHIER (LAFFITTE, PERMIN- GEAT et ROUTHIER 1963: 'Un metallotecte est un objet gtologique qui semble favoriser l ' tdi- fication d'un gisement ou d'une concentration mintrale') cannot be defined. This irregular though stratabound distribution is typical for many similar sulfate and sulfide deposits. We suggest, therefore, that the barite deposits of the Mts. de Cabri~res region (Southern France) originated through migration of and deposition from metal-bearing brines~during diagenesis involving silica, dolomite and barite. Consequently these deposits belong to the family of late diagenetic deposits.

Acknowledgements

The work for the present paper was initiated by suggestions of Prof. J. AriAs (Montpellier, France) and Dr. J. GLA~ON (Paris, France). Their continued interest is gratefully acknowledged. The author is also indebted for helpful criticism and suggestions to Prof. G. C. AMSTUTZ (Heiddberg) and to Dr. P. NICOLINI (Pan, France). The field work was started at the Laboratoire de Gtologie de l'Univer- sit6 de Montpellier and supported by a scholar- ship from the French Government and the Deutscher Akademischer Anstauschdienst. To both institutions the author wishes to express his appreciation. The manuscript was completed at the Mineralogisch-Petrographisches Instimt der Uni- versit~it Heidelberg. Laboratory data of much value have been contributed by Dr. H. PUCHELT (T~ibin- gen) and Dr. H. NIELSEN (Gtttingen). Their work is gratefully acknowledged.

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Proceed. Geol. Ass. Canada 11, 95--113 (1959). - - The logic of some relations in ore genesis. In:

Sedimentary ores: Ancient and Modern (Revis- ed). Proceed. 15th Inter-University Geological Congress, University of Leicester 1967, p. 13--29, 1969.

19 Mineralium Deposita, 4/8

274 TH. HOFFMANN, Barite Deposits of the "Montagne Noire", Southern France

- - , P. RAMDOHR, F. EL BAZ, and W. C. PAGE: Diagenetic behaviour of sulphides. Sedimen- tology and ore genesis. Developments in Sedimentology, Vol. 2, 65--90, Amsterdam: Elsevier 1964.

BOYER, F., et P. ROUTHIER: Observations sur deux niveaux min6ralis6s dans le Pal6ozoique inf6- rieur des Monts du Minervois (Montagne Noire, Aude). Bull. Soc. Geol. France (6) 8, 257--266 (1958).

- - , S. KRYLATOV, J. LE FEVRE et D. STOVVEL: Le D4vonien sup4rieur et la limite D6vono-Car- bonif~re en Montagne Noire (France), litho- stratigraphie -- biostratigraphie (Conodontes). Bull. Centre Rech. Pau -- S.N.P.A. 2, 5--33 (1968).

CHERMETTE, A.; Les ressources de la France en barytine. Bull. B.R.G.M. 2, 1-43 (1962).

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ENGEL*tAm3T, W. voN: Zum Chemismus der Po- renl6sung der Sedimente. Bull. Geol. Inst. Univ. Uppsala XL, 189--204 (1961).

GazE, B. : Etude g6ologique de la Montagne Noire et des C6vennes m&idionales. Mem. Soe. Geol. France 62, 1--215 pl. I--VII (1949a).

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Received 25. 9. 1968 / 20. 5. 1969

Dr. TH. HOFFMANN Mineralogisch-Petrographisches Institut der Universit~it, 6900 Heidelberg, Berliner StraBe 19